Rydberg atoms are highly excited atoms with intriguing properties. In the framework of quantum electrodynamics, the internal dynamics of a Rydberg atom in front of a surface are investigated in fourth order perturbation theory. For a pair of Rb Rydberg atoms in front of a perfectly conducting surface, a bound state with micrometer bond length, a Rydberg macrodimer, is predicted for a small window of surface distance. This leads to the possibility to use surface properties to actively tune interactions.<eng>
